1. Field of the Invention
The present invention relates to a catalyst for olefin polymerization that makes use of a novel modified methylaluminoxane preparation and to a method for producing such a modified methylaluminoxane preparation for use as the olefin polymerization catalyst, as well as to a method for carrying out olefin polymerization involving the use of the novel methylaluminoxane preparation as a polymerization catalyst component.
2. Description of the Related Art
The following patent publications and articles are incorporated herein by reference in their entirety: Japanese Patent Laid-Open Publications No. Sho 58-19309; Sho 60-35005; Sho 62-234009; Sho 63-234009; Sho 64-66214; Hei 1-207355; 2000-119278; 2000-119279; 2000-119280; Sho 60-260602; Sho 63-89506; Sho 63-178108; Hei 1-315407; Hei 2-22308; Sho 60-35006; Sho 60-35007; Sho 60-35008; Sho 61-108610 and Sho 61-296008; Macromolecules, 32, 9078 (1999); Journal of American Chemical Society (J. Am. Chem. Soc.) 118, 11664 (1996); and Organometallics 18, 65, (1999).
Aluminoxanes are condensation products generally prepared by partial hydrolysis of organoaluminum compounds and are known as a useful co-catalyst for the production of olefin polymers that can efficiently activate a transitional metal compound, a primary catalyst of the reaction. It is widely known that polymethylaluminoxane, which is made by using trimethyl aluminum as the organoaluminum material, is a particularly effective co-catalyst. Examples of these compounds are described in, for example, Japanese Patent Laid-Open Publications No. Sho 58-19309; Sho 60-35005; Sho 62-234009; Sho 63-234009; Sho 64-66214; and Hei 1-207355.
Modified aluminoxanes having two or more different types of alkyl groups have also been proposed: One type of modified aluminoxane disclosed in Japanese Patent Laid-Open Publications No. 2000-119278, 2000-119279 and 2000-119280 is produced by first mixing trimethyl aluminum with tetraalkyldialuminoxane that has alkyls with 2 or more carbon atoms and subsequently carrying out hydrolysis. The modified methylaluminoxanes synthesized using these techniques are soluble not only in aromatic hydrocarbon solvents but also in aliphatic hydrocarbon solvents and are, therefore, widely used in the production of olefin polymers for use in food products, for which use of aromatic solvents is restricted. Also, these modified methylaluminoxanes are highly stable while in storage. In addition, these compounds are synthesized through a mild reaction that can be readily controlled. However, the modified methylaluminoxanes made by the above-described techniques exhibit a lower activity than polymethylaminoxane and thus need to be improved.
Different techniques for solubilizing polymethylaluminoxane in aliphatic hydrocarbon solvents have been proposed in, for example, Japanese Patent Laid-Open Publications No. Sho 60-260602, Sho 63-89506, Sho 63-178108, Hei 1-315407, and Hei 2-22308. In a typical approach, polymethylaluminoxane produced in an aromatic hydrocarbon solvent is exposed to an alkylaluminum other than trimethylaluminum so as to increase the solubility of polymethylaluminoxane in the solvent. In this technique, however, when it is desired to replace the aromatic hydrocarbon solvent with an aliphatic hydrocarbon solvent, the aromatic hydrocarbon solvent is removed by taking advantage of its relatively high boiling point in the distillation under reduced pressure or other proper processes. In practice, as much as several percent by weight of the aromatic hydrocarbon solvent inevitably remains after the solvent replacement. Though effective in some cases at laboratory level, such a solvent replacement process is highly impractical for use in industrial applications.
A particular type of solid catalyst that is provided in the form of silica, alumina, magnesium chloride and other solid carriers carrying a transitional metal compound along with an aluminoxane has been in use. Several methods have been proposed concerning the use of such a solid catalyst component in the suspension polymerization or the gas phase polymerization. Examples of such methods are disclosed in, for example, Japanese Patent Laid-Open Publications No. Sho 60-260602, Sho 63-89506, Sho 63-178108, Hei 1-315407, and Hei 2-22308.
In most of the known examples mentioned above, polymethylaluminoxane is used as the aluminoxane in preparing the solid catalyst. Since trimethyl aluminum, the principal material of polymethylaluminoxane, is significantly more reactive than the other members of organoaluminum compound, it is difficult to control partial hydrolysis, and the insoluble, aluminum hydroxide-like inorganic aluminum compound resulting from the local hydrolysis can lead to a decrease in the yield as measured on the basis of aluminum atom. In addition, polymethylaluminoxane tends to become less soluble in the solvent as it undergoes association process. As a result, insoluble product is often formed, affecting the stability of polymethylaluminoxane during storage. For these reasons, there has been a large demand for the development of a novel modified methylaluminoxane that maximizes the yield as measured on the basis of aluminum atom while providing improved storage stability.
Since previously known modified methylaluminoxanes, when used in a catalyst using silica or other carriers, could only impart significantly lower activity to the solid catalyst than is achieved by polymethylaluminoxane, they have never been actively used in carrier catalysts. The cause of this low activity is believed to be that the amount of the alkylaluminum compound with alkyl group having 2 or more carbon atoms that was present in the modified methylaluminoxane and/or the amount of the modified methylaluminoxane with alkyl group having 2 or more carbon atoms were not suitable for the preparation of the carrier catalyst.
Recently, new catalyst systems for olefin polymerization were found in which a modified methylaluminoxane exhibits co-catalyst activity that is equivalent to, or even higher than, that of polymethylaluminoxane. As a result, application of modified methylaluminoxanes as co-catalyst for polymerization has attracted much attention. Examples of such system are described in Macromolecules, 32, 9078 (1999); Journal of American Chemical Society 118, 11664 (1996); and Organometallics 18, 65, (1999).